Field of the Invention
The present application is directed to integrated circuits and in particular to integrated circuits including inductors.
Description of the Related Art
In general, electronic oscillator circuits are used to generate repetitive oscillating electronic signals. A conventional tank circuit (i.e., an LC oscillator circuit) is a tuned circuit including an inductor coupled to a capacitor. Charge flows back and forth from the capacitor plates through the inductor so the tuned circuit can store electrical energy oscillating at its resonant frequency. An amplifier circuit compensates for small losses in the tank circuit to sustain oscillation. In general, the quality factor, Q, characterizes a resonator's bandwidth relative to its center frequency. Referring to FIG. 1, the quality factor of a typical parallel tank circuit may be represented as Q=1/(ωoLTANKGloss), where ωo is the resonant angular frequency of the tank circuit, LTANK is the inductance, and Gloss represents the conductive losses due to the inductor, the capacitor, and amplifier loading. A higher Q indicates a lower rate of energy loss relative to the stored energy of the resonator, i.e., oscillations die out more slowly. By supplying a transconductance, −Gm, that is equal and opposite to the tank losses (Gloss), the amplifier is able to sustain oscillation indefinitely at the resonant frequency of the tank and at an amplitude determined by the amplifier.